When I wander around Skyrim I'll often run into high elves with prisoners, rich lords on horses and sometimes named NPCs that I can interact with.

Unfortunately for them, the dragon born of their world loves stabbing and robbing in that order.

If the dragon born let them be, would they still wander from town to town or would they simply despawn at some point in time?

Edit
I've encountered a hunter and his horse on the road and held my blade. I followed him for some time and it appears that his entire existence consists of patrolling up and down the same 100 meters of trail. I was disappointed to say the least. Sfter some time has passed I shall return to the place whence I saw him last and see if he continues his drudgery.

Most locations in the game are respawning. This happens, depending on the location, at scheduled times. When a game location respawns, its enemies and loot are reset. This allows revisiting previously visited locations, which will have their contents reset.

In conclusion, I believe NPCs will not despawn until something causes them to die, or the location they're based in resets or respawns.

@galacticninja +1 for this. Another thorough answer. You could add unless a glitch occurs, everything is according to schedule. Even quest NPCs follow a schedule. But with a glitch, it is go back to a prior save. Just saying.
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ヴァイシャリSep 17 '12 at 18:16